In recent years, an ink-jet recording method has been applied in various printing fields such as photography, various printing, special printing such as marking and color filters, because it is capable of image formation in a simple manner at a low cost. In particular, image quality comparative to silver salt photography can be obtained by employing a recording apparatus to eject and control micro dots; ink having been improved in such as a color reproduction range, durability and ejection adaptability; and exclusive paper having been rapidly improved in such as coloring ability of colorant and surface glossiness. Image quality improvement of an ink-jet recording method of today can be achieved only when all of a recording apparatus, ink and exclusive paper are employed in combination.
However, in an ink-jet system requiring exclusive paper, there cause problems of limitation of a recording medium and cost up of a recording medium. Therefore, many attempts have been made to record on a medium, on which image is transferred, different from exclusive paper by an ink-jet method. Specifically, they are such as a phase transition ink-jet method which utilizes wax ink being solid at room temperature, a solvent system ink-jet method which utilizes a rapid drying organic solvent as a primary component, and an ultraviolet curable ink-jet method in which cross-linking by active rays such as ultraviolet rays (UV) is conducted after recording.
For example, ultraviolet curable ink includes radical polymerization type ultraviolet curable ink primarily comprising an acryl type composition (for example, refer to patent documents 1 and 2), and cationic polymerization type ultraviolet curable ink (for example, refer to patent document 3). Radical polymerization type ultraviolet curable ink has a problem of deterioration of curing ability due to sensitivity to an oxygen inhibition action under an environment including oxygen according to the polymerization mechanism. On the other hand a cationic polymerization type ultraviolet curable ink has a problem of easy progress of a dark reaction according to a property of the polymerization reaction resulting in viscosity increase during storage.
Further, as for a colorant in an ink-jet recording method, ink comprising primarily pigment being dispersed is often utilized in view of fastness of a formed image.
Generally, to achieve a stable dispersion characteristic, an important subject is how to achieve adsorption between a dispersant and pigment, and a non-polar interaction in the case of a polar dispersing solvent while a polar interaction in the case of a non-polar solvent is utilized. For example, in pigment dispersion of a solvent system, to utilize an acid base concept has been proposed. That is, a basic dispersant is utilized when pigment is acidic while an acidic dispersant is utilized when pigment is basic.
However, since ultraviolet curable ink utilizing a polymerizing compound as a dispersion solvent, though a solvent system, it is a system particularly difficult for adsorption between pigment and a dispersant due to a polar solvent arising from a polymerizing group being present, stable ultraviolet curable ink has not been obtained only by conventional technologies.
For example, in cationic polymerizing ultraviolet curable ink, an improving means against viscosity increase during storage described above is disclosed (please refer to, for example, Patent Document 4), however, stable dispersion cannot be achieved only by this technology and ejection becomes unstable when dispersion is unstable, which was a fatal problem as for ink-jet ink.
Patent Document 1: Unexamined Japanese Patent Application Publication No (hereinafter referred to as JP-A) 6-200204 (Claims, and Examples)
Patent Document 2: Japanese Translation of PCT International Application Publication No. 2000-504778. (Claims, and Examples)
Patent Document 3: JP-A 2002-188025 (pp. 2-7, and Examples)
Patent Document 4: JP-A 2004-2668 (Claims, and General description)